Chondroitinases are enzymes of bacterial origin that act on chondroitin sulfate, a component of the proteoglycans that are components of the extracellular matrix of a wide variety of tissues such as the central nervous system and for example they can mediate the attachment between the retina and the vitreous body of the human eye. Examples of chondroitinase enzymes are chondroitinase ABC I, SEQ ID NO: 37, which is produced by the bacterium Proteus vulgaris (P. vulgaris), and chondroitinase AC, SEQ ID NO: 5, which is produced by Flavobacterium heparinum. Chondroitinases ABC I SEQ ID NO: 37, and chondroitinase AC SEQ ID NO: 5, function by degrading polysaccharide side chains in protein-polysaccharide complexes, without degrading the protein core.
Yarnagata et al. (J. Biol. Chem. 243:1523-1535, 1968) describe the purification of the chondroitinases like ABC I SEQ ID NO: 37 from extracts of P. vulgaris. This enzyme selectively degrades the glycosaminoglycans chondroitin-4-sulfate, dermatan sulfate, and chondroitin-6-sulfate (also referred to respectively as chondroitin sulfates A, B, and C which are side chains of proteoglycans) at pH 8 at higher rates than it degrades chondroitin or hyaluronic acid. The products of the degradation are high molecular weight unsaturated oligosaccharides and an unsaturated disaccharide. However, chondroitinase ABC I, SEQ ID NO: 37, does not act on keratosulfate, heparin or heparitin sulfate.
Uses of chondroitinases include rapid, specific and non-surgical disruption of the attachment of the vitreous body to the neural retina of the eye, thereby facilitating removal of the vitreous body.
P. vulgaris chondroitinase ABC I SEQ ID NO: 1 migrates with an apparent molecular mass of about 110 kDa when resolved by SDS-PAGE. The appearance of a doublet in SDS-PAGE resolution of chondroitinase ABC has been reported (Sato et al., Agric. Biol. Chem. 50:4, 1057-1059, 1986). However, this doublet represents intact chondroitinase ABC and a 90 kDa degradation product. Commercial chondroitinase ABC protein preparations contain variable amounts of this 90 kDa degradation product and an additional 18 kDa degradation product also derived from chondroitinase ABC I, SEQ ID NO: 1.
Chondroitinase ABC II, SEQ ID NO: 26, has also been isolated and purified from P. vulgaris, Chondroitinase ABC II, SEQ ID NO: 26, is a polypeptide of 990 amino acids with an apparent molecular mass by SDS-PAGE of about 112 kDa. Its molecular mass as determined by electrospray and laser desorption mass spectrometry is about 111,772 daltons. Chondroitinase ABC II, SEQ ID NO: 26, has an isoelectric point of 8.4-8.45. Its enzymatic activity is distinct from, but complementary to, that of chondroitinase ABC I SEQ ID NO: 1. Chondroitinase ABC I, SEQ ID NO: 1, endolytically cleaves proteoglycans to produce end-product disaccharides, as well as at least two other products which are thought to be tetrasaccharides, Chondroitinase ABC II, SEQ ID NO: 26, digests at least one of these tetrasaccharide products from the chondroitinase ABC I (SEQ ID NO: 1) digestion of proteoglycan.
After a injury in the adult mammalian central nervous system (CNS), the inability of axons to regenerate may lead to permanent paralysis. An injury-caused lesion will develop glial scarring, which contains extracellular matrix molecules including chondroitin sulfate proteoglycans (CSPGs). CSPGs inhibit nerve tissue growth in vitro, and nerve tissue regeneration fails at CSPGs rich regions in vivo.
A number of molecules, and specified regions of them, have been implicated in the ability to support the sprouting of neurites from a neuronal cell, a process also referred to as neurite outgrowth. The term neurite refers to both axon and dendrite structures. This process of spouting neurites is essential in neural development and regeneration, especially after physical injury or disease has damaged neuronal cells. Neurites elongate profusely during development both in the central and peripheral nervous systems of all animal species. This phenomenon pertains to both axons and dendrites. However, neurite regrowth in the CNS decreases as the animal's age increases.
Chondroitinase enzymes have shown efficacy in improving functional outcomes in several in vivo models of spinal cord injury. Recombinantly produced chondroitinases AC (SEQ ID NO: 5) and chondroitinase B (SEQ ID NO: 12) polypeptides have shown efficacy in vitro by overcoming the barrier of an inhibitory substrate border, such as aggrecan, resulting in neurite extension for rat cortical neurons.
The inventors have discovered through a deletion analysis based on the available crystal structures, the minimally sized polypeptides capable of degrading chondroitin sulfate proteoglycans (CSPGs). The cleavage activity of all these mutants have been screened in vitro by zymographic assay using aggrecan as a substrate. A truncated polypeptide of chondroitinase AC (nΔ50-cΔ275), (SEQ ID NO: 11), lacking 50 and 275 amino acids from the amino and carboxy termini respectively and having a molecular weight of 38 kDa compared to 75 kDa of the full length protein, was found to be the minimal size that retained activity as tested by a zymographic assay. The deletion mutant of chondroitinase B (nΔ120-cΔ120), (SEQ ID NO: 17), lacking 120 amino acids from each of the amino and carboxy termini and having a molecular weight of 26 kDa compared to 52 kDa of the full length protein, was shown to retain activity as well in a zymographic assay. Reduction in the size and complexity of the molecule may facilitate diffusion to the site of action and potentially reduce immunogenicity for prolonged therapeutic use. These smaller chondroitinases could be potential therapeutics for spinal cord injury.
The present disclosure relates to mutants of chondroitinase genes, polypeptides and proteins derived therefrom, and their use in methods for promoting neurological functional recovery after central nervous system (“CNS”) injury or disease. The mutant genes, polypeptides and proteins derived from them preferably include deletion, substitution, or a combination of these from the structural units the mature gene or polypeptide; more preferably the mutant genes or polypeptides are deletion mutants of the mature gene or polypeptide. These mutant genes or polypeptides, preferably biologically active, may be used in various pharmaceutical compositions.
Polypeptide mutants of chondroitinase ABC Type I, SEQ ID NO: 1, Chondroitinase ABC Type II, SEQ ID NO: 26, Chondroitinase AC, SEQ ID NO: 5, and Chondroitinase B, SEQ ID NO: 12, are provided. Other mammalian enzymes mutants with chondroitinase-like activity may independently include such enzymes as hyaluronidase 1, SEQ ID NO: 30, hyaluronidase 2, SEQ ID NO: 31, hyaluronidase 3, SEQ ID NO: 32, hyaluronidase 4, SEQ ID NO: 33, and optionally PH-20, SEQ ID NO: 34. These deletion or substitution mutant may be used alone or in combination with chondroitinases or their deletion or substitution mutants as therapeutic compositions and mixtures. Further provided is the use of these mutants, and preferably the chondroitinase deletion or substitution mutants to promote neurological functional recovery in mammals following injury to the CNS, including but not limited to contusion injury.
One embodiment of the present invention are isolated nucleic acid molecules consisting of, and preferably comprising, a nucleotide sequence encoding the amino acid sequence of polypeptides that are deletion and or substitution mutants of proteoglycan degrading molecules. Independently, nucleic acid molecules of the present invention may encode for mutant proteoglycan degrading polypeptides of chondroitinase ABC Type I, SEQ ID NO: 1, Chondroitinase ABC Type II, SEQ ID NO: 26, Chondroitinase AC, SEQ ID NO: 5, and Chondroitinase B, SEQ ID NO: 12, hyaluronidase 1, SEQ ID NO: 30, hyaluronidase 2, SEQ ID NO: 31, hyaluronidase 3, SEQ ID NO: 32, hyaluronidase 4, SEQ ID NO: 33, or optionally PH-20, SEQ ID NO: 34 and combinations of these. Preferably the nucleic acids encode for chondroitinase deletion and or substitution mutants. The invention is also directed to nucleic acid molecules consisting of, and preferably comprising, a nucleotide sequence complementary to the above-described nucleic acid sequences. Also provided for are nucleic acid molecules at least 80%, preferably 85% or 90%, still more preferably 95%, 96%, 97%, 98%, or 99% identical to any of the above-described nucleic acid molecules. Also provided for are nucleic acid molecules which hybridize under stringent conditions to any of the above-described nucleic acid molecules. The present invention also provides for recombinant vectors comprising these nucleic acid molecules, and host cells transformed with such vectors.
Also provided are isolated polypeptides consisting of, and preferably comprising, the amino acid sequence of deletion and or substitution mutants of proteoglycan degrading polypeptides. Independently, proteoglycan degrading polypeptides can include chondroitinase ABC Type I, SEQ ID NO: 1, Chondroitinase ABC Type II, SEQ ID NO: 26, Chondroitinase AC, SEQ ID NO: 5, and Chondroitinase B, SEQ ID NO: 12, hyaluronidase 1, SEQ ID NO: 30, hyaluronidase 2, SEQ ID NO: 31, hyaluronidase 3, SEQ ID NO: 32, hyaluronidase 4, SEQ ID NO: 33, optionally PH-20, SEQ ID NO: 34. Preferably the polypeptides are deletion mutants of chondroitinases. Pharmaceutical compositions may be prepared from the mutant proteoglycan degrading molecules such as chondroitinases and or hyaluronidases; the composition may include one or more of the deletion and substitution mutants from different proteoglycan degrading polypeptides.
In one aspect of the invention, biologically active proteoglycan degrading polypeptide are provided having a deletion or substitution of at least one amino acid. The mutant proteoglycan degrading polypeptides include those having the minimal size yet retain a degree of activity as determined by the enzyme assays described in the specification. Preferred deletion or substitution mutants of the proteoglycan degrading molecule are those which degrade chondroitin and have one or more amino acid deletions from the N-terminus, about 1-120 amino acids and/or the C-terminus, about 1-275 amino acids, more preferably the deletions are from a chondroitinase.
One aspect of this invention are deletion and or substitution mutants of proteoglycan degrading polypeptides, preferably deletion mutants of chondroitinase polypeptides, that promote neurite regeneration and or plasticity in the CNS and or promote or inhibit the diffusion of therapeutic molecules into tissues by degradation of proteoglycans.
The mutant proteoglycan degrading polypeptides, preferably deletion and or substitution mutants of chondroitinases, may promote neurite regeneration in the CNS and or promote or inhibit the diffusion of therapeutic molecules into tissues by degradation of proteoglycans and can be obtained through expression of suitably modified DNA sequences. Thus, the present invention also provides suitable expression vectors and host cells compatible therewith.
In yet other aspects, the invention comprises pharmaceutical compositions that include biologically active polypeptide of deletion and or substitution mutants of proteoglycan degrading molecules, and preferably deletion or substitution mutants of chondroitn degrading polypeptides as described above, in combination with a pharmaceutically acceptable carrier.
The deletion mutants and or substitution mutants of the proteoglycan degrading polypeptides of the present invention may be used to promote the regeneration of neurites in nerve tissue. These mutants might also be useful in the treatment of other CNS disorders in which plasticity, regeneration, or both might be beneficial. For example CNS injuries and disorders may include but not limited to contusion injury, traumatic brain injury, stroke, multiple sclerosis, brachial plexus injury, amblioplia. Because of their proteoglycan degrading properties, they may be used to promote the delivery of therapeutic compositions and diagnostics to tissues and cells that are normally impermeable to them. Alternatively, they may be used to inhibit penetration of therapeutic compositions, diagnositics or cells to tissues that use part of the extracellular matrix to enter tissues. Because of their smaller size compared to the full length enzyme, the deletion and or substitution mutants are easier to make and easier to deliver to target cells and tissues. These and other even smaller deletion or substitution mutants of proteoglycan degrading molecules could be used as potential therapeutics with lesser immunogenicity and similar or higher tissue penetration ability for the treatment of CNS injury.
The deletion mutants may offer significant advantages over the full length proteins in the therapeutic development process. The tissue penetration of the enzymes may be significantly effected by the protein size. The effect of protein size on tissue penetration is difficult to predict, but dependent on size and charge. The rate of penetration depends on tissue composition, charge interactions and hydration effects. Having active enzymes of widely ranging size may allow selection of an enzyme based on optimal tissue penetration properties, perhaps maximizing effective concentrations or limiting peripheral exposure to the enzyme.
The immune response of a mammal to a bacterial protein may or may not limit the ability to use the protein or polypeptide as a therapeutic. The generation of antibodies to the protein can restrict repeated exposures, as well as potentially inactivate the protein therapeutic making it ineffective. The smaller mutant proteoglycan degrading enzymes, preferably mutant chondroitinase enzymes, may limit the antigenic sites, limit an immune response or at least simplify the process of engineering an enzyme with reduced immunogenicity.
The release rate of proteins from matrices often used in sustained release formulations can be dependent upon size and cross-linking. The effective release rate of deletion mutants of proteoglycan degrading polypeptide from the matrix can be engineered through the manipulation of the size of the enzyme. Having a repertoire of chondroitinase enzymes of various size and charge will give an significant advantage for the development of a sustained release formulations.